This invention relates generally to a directional coupling system, and, more particularly, to a directional coupler which incorporates therein a holographic element.
The need frequently arises for communications or data transmission systems to convey a message from an information source (master) in one location to a multiple number of users at another location. In addition, such a system must be capable of sending information back to the master source, while at the same time preventing any of the users from intercepting data from any of the other multiple users. The directional coupler allows all of the energy in the optical signal from any one of the users to be transmitted back to the master source with 100% efficiency, but allows only a controlled amount of the energy from the master source to be transmitted to any one user; hence the name directional coupler.
In recent years with the development and implementation of fiber optic technology into practical communication systems, a great deal of attention has been given to the coupling and distribution of fiber optic signals. Size and fabrication expense are critical factors when providing coupling devices. To date, however, directional couplers have been either unreliable in complete separation of the individual signals, or are of such a size and cost so as to provide an overall system which is incompatible with the required small size and economic requirements. Consequently, a need arises for a small, lightweight, inexpensive directional coupler which can be effectively used as a directional coupling device in a fiber optic system.